Reaktion #683082

Reaktionsgleichung

diphenylphosphoryl azide

5-methylpyrazine-2-carboxylic acid

tert-butanol

DPPA

Et3N

→

tert-butyl 5-methylpyrazin-2-ylcarbamate

Lösungsmittel

1,4-dioxane

Reaktionsbedingungen

Aufarbeitung

1. 1
   Sonstigeat 95° C.
2. 2
   Temperaturheated for additional 1.5 h
3. 3
   TemperaturThe reaction mixture was cooled down
4. 4
   Einengenconcentrated
5. 5
   workup.ADDITIONthe residue was diluted with EtOAc (50 mL)
6. 6
   Waschenwashed with water (30 mL), 3 M NaOH (30 mL), sat. NaHCO3 (30 mL) and brine (30 mL)
7. 7
   Trocknendried over Na2SO4
8. 8
   Einengenconcentrated
9. 9
   SonstigeThe residue was purified

Vorschrift

To solution 5-methylpyrazine-2-carboxylic acid (2.5 g, 18.1 mmol), tert-butanol (6.92 mL, 72.4 mmol), Et3N (3.78 mL, 27.1 mmol) in 1,4-dioxane (12.5 mL) at 95° C. was dropwise added diphenylphosphoryl azide (DPPA, 3.23 mL, 18.1 mmol), and the reaction was heated at 95° C. for 1.5 h, followed by a 2nd portion of DPPA (1 mL, 5.6 mmol) and heated for additional 1.5 h. The reaction mixture was cooled down, concentrated and the residue was diluted with EtOAc (50 mL), washed with water (30 mL), 3 M NaOH (30 mL), sat. NaHCO3 (30 mL) and brine (30 mL), dried over Na2SO4, and concentrated. The residue was purified by flashed chromatography on silica gel eluting with gradient EtOAc/CH2Cl2 (0-20%) to afford tert-butyl 5-methylpyrazin-2-ylcarbamate as white solid. LCMS (m/z): 210.1 (MH+), 0.69 min; 1H NMR (400 MHz, CDCl3) δ ppm 9.17 (s, 1H), 8.09 (s, 1H), 7.75 (br. s., 1H), 2.51 (s, 3H), 1.56 (s, 9H).

Quelle